This patent application describes a cobalt alloy thin film magnetic disk having a sputter deposited, single element, chromium underlayer, of a thickness 50 to 200 Angstroms (A), which presents the (100) (one,zero,zero) plane of the chromium atoms at a layer's surface. The cobalt alloy is sputter deposited on this chromium underlayer, such that the (110) plane of the cobalt alloy, and thus the C axis of the cobalt alloy, are parallel to the disk's recording surface, thus facilitating operation of the disk in longitudinal, binary data, recording systems.
The magnetic properties of a thin film magnetic recording layer, for example the coercivity thereof, must be tightly controlled in order for the magnetic recording disk to meet the design specifications of a particular DASD device, which DASD device is in turn used to store digital data in conventional data processing installations.
A goal in the fabrication or manufacture of thin film magnetic recording media is to obtain magnetic properties that are compatible with, and indeed are required by, the read/write transducing head of the DASD unit in which the media will be used.
A number of means have been practiced in the art to control the magnetic properties of thin film magnetic media. Examples are, the use of different materials directly under the thin film magnetic layer, variation in the thickness of the magnetic layer, and the use of different magnetic alloys in the magnetic layer. However, the art has generally not succeeded in controlling the bulk magnetic properties of the thin film magnetic layer for a given set of material and thickness requirements for the magnetic layer.
U.S. Pat. No. 4,749,459, incorporated herein by reference, describes a number of ways by which the coercivity of a thin film magnetic recording layer may be controlled, including forming the magnetic film on a chromium underlayer and controlling the magnetic film's coercivity by controlling the thickness of the underlayer, controlling the amount of platinum in the magnetic film, and sputtering the magnetic film in an atmosphere that includes argon and a trace amount of a selected gas such as nitrogen, ammonia, or oxygen and nitrogen.
U.S. Pat. No. 4,654,276, incorporated herein by reference, is directed to improving the coercivity of a magnetic layer by the use of a nonmagnetic underlayer of tungsten (W) between a substrate and a cobalt-platinum (CoPt) or a cobalt-platinum-chromium (CoPtCr) magnetic layer. This patent also point out that the coercivity of a CoPt magnetic film can be improved by the use of a Cr underlayer, that W has been used as an enhancement layer in certain types of thin film disks, that a layer of an intermetallic compound such as cobalt-tungsten (Co.sub.3 W) has been used to form a nucleating layer for a subsequently deposited magnetic film, and that a CoPt magnetic layer has been formed on a nonmagnetic layer of a tungsten-cobalt (WCo) alloy.
U.S. Pat. No. 4,079,169, incorporated herein by reference, describes a magnetic recording disk, and recognizes that a clad layer is normally deposited on the substrate member, before a magnetic layer is deposited thereon. This clad layer provides wear resistance and mechanical rigidity, provides an easily polishable layer, protects the underlying aluminum from corrosion, and that this clad layer, as well as any other underlayers, should enhance the coercivity and other magnetic properties of the overlying magnetic thin film layer. The specific cobalt based alloy clad layer that is described comprises 10-30% chromium, from 8-18% tungsten, from 8-30% nickel, the remainder being cobalt. The function of the cobalt and the chromium in this clad layer is to provide corrosion resistance. The function of the tungsten in this clad layer is to provide hardness and rigidity. The function of the nickel in this clad layer is to provide ductility.
The above mentioned related patent application describes a cobalt alloy thin film magnetic disk having a sputter deposited, single element chromium underlayer.
While the various means practiced in the art for controlling the magnetic properties of thin film magnetic recording media have been generally useful, there remains a need in the art for an underlayer of simple construction whereby these magnetic properties can be controlled independent of controlling the magnetic properties of the magnetic layer itself, and independent of factors such as layer thickness.
The present invention provides such an underlayer in the form of a thin, sputtered, underlayer of a nonmagnetic, binary, chromium-tungsten (CrW) alloy whose major constituent is chromium, and preferably of a Cr88%,W12% composition, upon which the thin film magnetic recording layer is subsequently deposited.